Download g.The Endocrine System

The Endocrine System
(exocrine vs endocrine glands)
all major endocrine glands are richly supplied with blood capillaries
no clear distinction between nervous and endocrine
systems
2. most, if not all, organs produce hormones
“officially” the endocrine system consists of several major glands
and many minor glands
=neuroendocrine system
3. Hormones are secreted in response to specific
stimuli
they are intimately interrelated
! complement each other
! two ends of a single spectrum
3 mechanisms: neural, humoral, hormonal
A. Humoral
The Neuroendocrine System
Nervous System
hormones secreted in direct response to changing
blood levels of certain chemicals in blood
Endocrine System
localized effects: cell to cell
targets: neurons, muscle cells or glands
transmission by nerve impulses
uses chemical signals only cell to cell
immediate response (ms to seconds)
short lived (ms to minutes)
widespread effects: throughout body
targets: all organs and tissues
transmission as hormone through blood
uses only chemical signals
gradual response (seconds to hours)
longer lived (minutes to days)
affect endocrine gland directly
B. Neural
Both
both involved in coordination & control
both produce biologically active chemicals
some parts of brain are glands/some glands are nervous tissue
some responses begin as nervous reflex and end as hormonal responses
hormones secreted due to direct nervous stimulation
C. Hormonal
General Characteristics of Hormones
Anterior Pituitary = master gland
1. a chemical is considered a hormone if it is secreted
and transported in the blood
secretes several hormones that control the secretion of
other endocrine glands
! Tropic Hormones
same chemical can also be a neurotransmitter, or
lymphokine, etc
4. Many endocrine glands secrete more than one
hormone
the major hormones are secreted from ductless
glands directly into blood
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
hormones can be secreted independently of one another
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5. hormone effects are highly specific to “target
organ”
! requires specific binding site
(receptor proteins)
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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! synergistic effects
= presence of 1 enhances effects of other
! antagonistic effects
= 1 counteracts effects of other
even though every hormone comes in contact with every cell
! permissive effects
receptor can be on the surface of the target cell or inside the
target cell
= one hormone “primes” target organ for another
hormone;
target cells respond only to specific hormones
8. Hormones don’t accumulate in blood
6. At the cellular level each hormone can affect a
target cell in only a few ways:
those that bind to target cells are destroyed
a. can change in cell membrane permeability
! half-life ~ seconds – 30 minutes
excess are continually cleared by liver and kidney
eg. change in secretory activity of a cell
b. can alter metabolic pathway(s)
therefore for prolonged effect
eg. enzymes activated or inactivated
! make new products
! cease making product
! hormones must be continuously secreted
c. can change rate of cell division
eg. speed up or slow down
Maybe different effects in different target cells for
same hormone
7. Most cells have receptors for more than one type
of hormone
hormones can interact with each other
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Major Endocrine Glands
! in women: stimulates follicles to begin
growing to ovulation
Pituitary Gland (=Hypophysis)
! in men: stimulates development of
seminiferous tubules and sperm cells
small but extremely important structure
d. Leutinizing Hormone (LH)
attached to a stalk (infindibulum) at base of
hypothalamus
! in women:
final maturation of follicle
housed in sella turcica of sphenoid bone
stimulates formation of corpus luteum
consists of two separate glands
[a temorary endocrine gland of pregnancy]
Anterior Pituitary Gland
promotes secretion of progesterone
master gland
! in men:
stimulates interstitial cells to secrete
hormone = testosterone
secretes tropic (or trophic) hormones:
a. Thyroid Stimulating Hormone (TSH)
if pituitary gland is removed by radiation or surgery, need
hormone treatment rest of life or some other glands will
shut down
! stim development and secretions from
thyroid gland
in addition to tropic hormones, Ant Pit also secretes
some other (nontropic) hormones:
b. Adrenocorticotropic Hormone (ACTH)
e. Growth Hormone (GH)
! normal growth and development of adrenal
cortex
promotes growth of bone and soft tissue
c. Follicle Stimulating Hormone (FSH)
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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! stim protein synthesis
Posterior Pituitary Gland
amt of GH secreted decreases with age
hormones released by direct nervous stimulation of
posterior pituitary
HYPERSECRETION of GH
during childhood
! gigantism
during adulthood
! acromegaly
a. Antidiuretic Hormone (ADH,
enlargement esp of bones of hands, feet,
jaws and cheeks
=vasopressin)
(=against production of urea)
HYPOSECRETION of GH
during childhood
! dwarfism
f. Prolactin (PRL;
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
ADH is released whenever receptors indicated
dehydration
ie. decreases urine output
conserves water
= Lactogenic Hormone)
affects female:
b. Oxytocin
! induces breast development during
pregnancy
(=swift childbirth)
stimulates contraction of uterine muscles
during labor
! initiates milk secretion after childbirth
prl release is stimulated by suckling
causes milk ejection into ducts as result of
nursing infant [let down reflex]
no significant functions in males
triggered by neural stimulus: suckling
functions in “societal memory”: affects ability
to recognize & trust others
[deficiency may be correlated with autism]
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Pineal Gland
Thymus
located behind the midbrain and 3rd ventricle
attached to roof of third ventricle
a temporary endocrine gland
behind sternum, below thyroid
not sure of all its functions in humans but seems to
regulate cyclic activities
large in fetus and child
maximum size at puberty
degenerates in adult (replaced with fat)
Rene Descartes (1596-1650) thought it was the seat of
the human soul
functions as endocrine gland and as part of immune
system
is light sensitive ! monitors photoperiod
a. Melatonin
secretes thymosin and related hormones
main hormone it secretes is melatonin
light suppresses production
dark stimulates production
! stimulates development of lymphatic organs
!secretion rises at night, fluctuates seasonally
and with changing day length
! induces maturation and development of WBC’s
particularly T-lymphocytes
in lower animals it helps regulate cyclic activities:
hibernation
estrous
migration
In humans:
! may help regulate menstrual cycle
! inhibits onset of puberty in males
may be related to seasonal affective disorder and
PMS
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
Thyroid Gland
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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HYPERSECRETION of Thyroid Hormones
!Graves disease
up to 30% increase in Metabolic Rate
! appetite
weight loss
nervous irritability
the largest endocrine gland in adults
surrounds trachea just below larynx
consists of 2 lobes !usually described as butterfly
shaped
HYPOSECRETION of Thyroid Hormones
During growing years
! cretinism
low metabolic rate
retarded growth and sexual devel
often mentally retarded
Hormones:
a. Thyroid Hormones (T3, T4)
As adult
! Myxedema
loss of mental and physical vigor
weight gain
thickened skin
activated by TSH from Ant Pit
contain Iodine atoms
98% of body’s Iodine is in the thyroid gland
b. Calcitonin
inadequate iodine in diet ! goiter
thyroid hormones help to regulate metabolism
in all cells:
! increases metabolic rate & ATP production
! increase oxygen consumption and bld O2 levels
! promotes maturation and development of the
nervous system
! increases protein synthesis
!help maintain normal reproductive function
many environmental stimuli can inhibit
secretions of this gland:
decreases blood Ca++ / promote bone
deposition by
inhibiting osteoclasts
stimulating osteoblasts
its effects are significant only in children,
negligable effect in adults
HYPOSECRETION of Calcitonin
can cause ricketts in children
(but usually due to Ca+ + or Vit D deficiency)
cold temp, physical stressors, noxious stimuli
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Parathyroid Glands
Pancreas
small round bodies attached to the posterior surfaces
of the thyroid gland
both an exocrine and endocrine gland
exocrine (98% of mass of pancreas):
secretes digestive enzymes
usually 4 or 5, but varies
a. Parathyroid Hormone (PTH)
endocrine (<2% of mass of pancreas):
contains clusters of endocrine cells
helps maintain homeostasis of blood calcium
= Islets of Langerhans
antagonist to calcitonin
(~1 Million clusters; each up to several 1000 cells)
raises blood Ca++ levels:
humoral regulation: monitors blood glucose conc
& amino acid levels
++
!promotes Ca absorption by kidney
tubules and intestine
mainly secretes:
insulin
glucagon
! stimulates osteoclasts to dissolve bone
since bone contains both calcium and phosphorus
this releases both into blood
Calcium homeostasis is important in:
neuromuscular function
blood clotting
synapses
to activate certain enzymes
affects cell membrane permeability
regulate blood sugar levels
both are proteins
a. Insulin
levels rise immediately after a meal
!moves glucose, amino acids and fatty
acids out of blood, into cells (except liver
surgical removal of thyroid gland requires PTH hormone replacement
therapy if all parathyroids are removed at the time
cells)
!lowers blood glucose concentrations
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Diabetes
only brain, liver and red blood cells do not
need insulin to take up glucose
diabetes is a general name for a group of diseases
b. Glucagon
two major varieties:
diabetes insipidus
diabetes mellitis (Types I & II)
secretion rises between meals
acts mainly on liver
Diabetes insipidus
glucose synthesis
and release into blood
a disease associated with Posterior Pituitary
!increases blood glucose concentration
deficiency in ADH causes low reabsorption of water
antagonist to insulin
large volumes of dilute urine are produced:
both hormones maintain constant blood glucose levels
! to feed brain cells esp
(up to 10 gallons/day vs normal 1 qt/day)
leads to electrolyte imbalances etc
! to provide energy for all body cells
Diabetes mellitis
secretion of hormones directly controlled by blood
sugar levels:
most common of all endocrine disorders
!18.2 Million (2004) diabetics in US,
after meal ! high blood sugar ! insulin
5-6 Million more may be borderline diabetics
fasting ! low blood sugar ! glucagon
diabetes is 7th leading cause of death & leading cause
of blindness in US
!40,000 die anually as result of disorder
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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diabetes is a group of disorders characaterized by
high blood glucose concentrations
decreased glucose utilization
levels of glucose build up in blood
caused by:
since glucose can’t be used alternate fuels are
mobilized:
inadequate insulin secretion by beta cells in Islets
=Type I
increased fat mobilization
fats in blood rise to up to 5x’s normal
as cells shift to fat catabolism
! produce ketone bodies
! lower blood pH = acidosis
! acetone breath
! increased risk of atherosclerosis
lack of response by target cells to insulin
=Type II
10% = Juvenile Onset Diabetes (Type I)
90% = Maturity Onset Diabetes (Type II)
without insulin to stimulate protein
synthesis they are instead broken
down and converted to glucose in cells
Type I: Insulin Dependent Diabetes Mellitis
! tissue wasting
usually develops during adolescence
high levels of glucose in blood lead to large
quantities of glucose spilling into urine
is an autoimmune disorder triggered by 2 factors:
1. genetic component ! susceptibility
2. environmental component ! still unknown,
may be viral
! diagnostic test for disease
(used to taste it, now have chemical indicators)
results in malfunction of Islet cells in pancreas
!dramatic decrease in the number of beta
cells
! this draws large amts of water into urine
Type 2, Non Insulin Dependent Diabetes Mellitis
!insulin is not produced in sufficient quantities
results in all body cells (target cells):
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causes are poorly understood:
most are obese ! but its not obesity per se
seems to be a strong genetic component
also associated with a sedentary lifestyle
target tissues become less responsive to insulin
= insulin resistance
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effects:
reduces life expectancy by ~1/3rd
25 x’s greater rate of blindness
17 x’s greater rate of kidney disease
17 x’s greater rate of gangrene
2 x’s greater chance of heart attack
Immediate (Acute) Complications of both forms
hyperglycemia, ketoacidosis, electrolyte
imbalances (as cations such as Na+ and K+
accompany ketones into urine)
Chronic Secondary Complications
often involve gradual changes over years
most common changes occur in vascular system
1. narrowing of large blood vessels in brain,
heart and lower extermities
! can result in stroke, heart attack or
limb loss
2. lesions in microvasculature are common
leads to development of scar tissue
! especially affect kidneys and eyes
3. impaired nerve function
esp autonomic fibers and peripheral
sensory fibers
leads to altered GI , bladder function and
impotence
and loss of sensation esp in lower limbs
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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and excreting K+
Adrenal Glands
on top of kidneys
3. this also indirectly regulates water
reabsorption
divided into cortex and medulla which function as two
separate glands
[more salt reabsorbed ! more water reabsorbed]
HYPOSECRETION by Adrenal Cortex
Addison’s Disease
due to inadequate mineralocorticoids &
glucocorticoids
Adrenal Cortex
cortex = outer layer of adrenal gland
!comprises 80 –90% of adrenal gland
b. Glucocorticoids (95% = cortisol
(hydrocortisone))
absolutely essential for life
regulated mainly by ACTH from Ant. Pituitary
affect every cell in body
secretes 30 - 50 different hormones
secretion follows circadian rhythm
all hormones secreted by adrenal cortex are steroids
! highest ~8:00am; lowest ~12:00am
1. generally raise blood glucose levels:
all are made from cholesterol
2. inhibit inflammation and tissue destruction
also immunosuppressive
these hormones can be categorized as 3 different
kinds:
3. additional effects on
a. Mineralocorticoids (90% = aldosterone)
! aldosterone increases salt and water
reabsorption by kidneys
blood pressure
immunity
wound healing
fetal devel of brain and lungs
maintains constant blood Na+ levels
by reabsorbing Na+ in kidney if needed
Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Adrenal Medulla
HYPOSECRETION of Mineralocorticoids
Addison’s Disease
Kennedy had mild form
low ACTH may also produce this
symptoms:
bronzing of skin
kidney impairment
water retention
increased blood pressure
weight loss
apathy
cannot cope with stress
immunosuppression
hypoglycemia
lethargy and muscle weakness
unlike cortex, is not essential for life
secretes epinephrine and norepinephrine
(=catecholamines)
also neurotransmitters of sympathetic NS
!affect same structures as sympathetic NS:
heart
smooth muscle
glands
HYPOSECRETION of Mineralocorticoids
Cushing’s Syndrome
weakens skin and muscles
serves to prolong or increase effects initiated by
sympathetic NS.
c. Sex Hormones
(=gonadocorticoids; eg. DHEA,
estrogen, progesterone, testosterone)
androgens:
promote protein synthesis
normally not masculinizing
female hormones:
HYPERSECRETION of gonadocorticoids
women in early puberty:
adrenogenital syndrome
masculinizing effect
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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Minor/Temporary Endocrine
Glands
Ovaries & Testes
endocrine and reproductive function
Kidneys
secrete steroid hormones
secrete most (85%) erythropoietin
the same gonadotropins that are found in adrenal cortex
affect development and maturation of reproductive
organs and reproductive behavior
! stimulates RBC production in bone marrow
Liver
Steroid Abuse
secretes ~ 15% of body’s erythropoietin
stimulates RBC formation
Taking large amounts of Androgens (steroids):
has negative feedback effect on FSH & LH
! almost shuts down
! decreased sperm production
! temporary or permanent sterility
! increased cancer risk
Heart
atria contain some specialized muscle cells that
secrete Atrial Natriuretic Peptide (ANP)
also when large amounts are take some is
transformed into estrogen
! reduces blood volume, pressure, Na+
conc
! breast enlargement
Stomach & Duodenum
mucosal lining secretes several hormones to help
control digestion:
gastrin
enterogastrone
secretin
cholecystokinin
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regulates secretion of:
gastric juices
pancreatic enzymes
bile
Adipose Tissue
releases leptin
after uptake of glucose and lipids which is
converted to fat
leptin binds to CNS neurons in hypothalamus
! produces sensation of satiety
Placenta
acts as temporary endocrine gland during
pregnancy
releases 3 hormones:
a. chorionic gonadotropic hormone (CGH)
! maintains hormonal activity of ovary
pregnancy test
b. estrogens & progesterone
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Human Anatomy & Physiology: Endocrine System; Ziser, 2010.4
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